Hey, Tad. See my post here:
92 Gmc Jimmy 4.3 Ltr Cfi Problems!?!
Perhaps it's not likely but if you have an intermittent ground causing the problem you might check the insulation on the wire bundle coming through the firewall near the shift linkage. I'd bet the wires for the wiper are in there. The tranny problem I had drove me nuts for a while before I thought to trace the wires.
As I said, not likely but if you are otherwise stumped it can't hurt to check this and/or trace out other wiper wires.